With reference to FIG. 1, caster rolls 10 control and guide the progress of a billet or slab 12 of steel that is produced by a caster. Caster rolls wear because of corrosion, abrasion, plastic deformation and thermal fatigue and cracking. Repairing caster rolls can minimize the need for costly shutdowns and prevent expensive breakdowns.
The repairing or rebuilding of caster rolls involves depositing an alloy in the area of the caster roll that is being repaired. Typically, a tubular metal-cored wire is deposited on the caster roll via submerged arc welding. Layers of alloy can be deposited on the caster roll; the layers include a butter pass, buildup layer(s), and hardfacing layer(s). For ease of understanding the figures, the individual layers are not depicted in FIGS. 2, 3 and 4. After the caster roll has been hardfaced, the alloy that was deposited on the caster roll undergoes many stresses and strains when the caster roll is put back on line guiding hot steel.
As mentioned above, the caster roll 10 guides a hot billet or slab of steel 12. With reference to FIG. 2, for a hardfaced caster roll 10, alloy that has been deposited over the surface of the roll is heated along a line of contact 16 with the hot steel. With reference to FIG. 3, the heated hardfacing alloy along this line of contact 16 tries to expand in all directions, but it is confined by the roll body in all directions, except that it can expand up into the hot billet or slab of steel 12 when the alloy comes in contact with the steel. This expansion is possible because the steel is plastic while hot. The line of contact 16 does not expand in other directions because it is confined by the body of the caster roll. As the alloy along the line of contact 16 expands up into the hot steel, the alloy along the line of contact is under compression because of the mass of the remainder of the roll. As the caster roll 10 rotates, the alloy that was along the line of contact 16 no longer contacts the hot steel billet or slap 12. With reference to FIG. 4, the side of the caster roll 10 not in contact with the hot steel is typically sprayed with relatively cool water which also results in cooling of the hardfacing alloy and especially the alloy along the line of contact 16. The cooling of the alloy along the line of contact 16 results in the alloy contracting. This contraction causes tensile stresses. This cycle of compression while heating, followed by tension while cooling, is repeated along the line of contact 16 each time the roll rotates a full turn.
It is desirable to develop a test method to evaluate an alloy used to hardface caster rolls to determine the alloy's ability to withstand the thermal cycling discussed above.